Yes, absolutely 3.x is still being updated.
Admittedly at this stage it's mostly me 😃 supporting 3.x, but there are other contributors who bring in new PRs / backports / bug fixes.
3.6 is the current stable branch, we recently built 3.6.1 and there will likely be new builds soon for Android requirements for Google Play.
3.7 is the current feature branch, we'll be making a the first dev version soon (lots of features still to go though, it's a longterm project, but I'm aiming to keep the dev / beta version very usable).
You can't necessarily go by the commits, because bug fixes are often small (<50 lines of code) where for instance the current PR I'm working on is 6K lines of code, and I have another with 15K lines of code. Feature PRs tend to be bigger and take more time (weeks / months). If there aren't many commits, it's usually because I'm working on bigger areas and can't afford the interruptions for smaller PRs.
For example, when automatically re-importing a series of graphics files that I have updated, the progress bar tends to freeze about 1/4 of the way through, even though the import process is working and it eventually finished. Not a deal killer but annoying.
For bugs, these need to be reported on github, and need to be on the radar, which means they need to be correctly milestoned (3.x or 3.7) and preferably on the 3.x triage project.
Some older bugs will have slipped off the radar, unless they get bumped, it isn't obvious they are a bug fix priority, so feel free to bump bugs. I try and have a go at most, although some are outside my areas.